Spintronics M1 Nano

pages

Documents

Écrit par
Laurent

Publié par
larec

Lire

Le téléchargement nécessite un accès à la bibliothèque YouScribe Tout savoir sur nos offres

pages

Documents

Lire

Le téléchargement nécessite un accès à la bibliothèque YouScribe Tout savoir sur nos offres

Publié par

larec

Nombre de lectures

Poids de l'ouvrage

1 Mo

Niveau: Supérieur, Master, Bac+4
Spintronics M1-Nano 1 Chapter V: spintronics • Magnetism and itinerant magnetism •Giant magnetoresistance •Hard disks magnetic heads •Spin valve effect •MRAM's

spintronics m1-nano

spin symmetries

babags rrrrrrrr

??? ???

atoms

screens repulsion between

magnetic exchange

spatial spin

Voir

Publié par

larec

Nombre de lectures

Poids de l'ouvrage

1 Mo

??? ???

ChapterV: spintronics•Magnetismanditinerantmagnetism•Giantmagnetoresistance•Hard disksmagneticheads•Spin valve effect•MRAM’sSpintronicsM1-Nano1

r⊗ψχ)(ψψψψψ121221=−−−−−rrrrrrrrrRrRrRrRXEABABsnoineewtebnoislupersneercs egrahcnortcele SG nI,ψψrrSGXErr)()( niygrene bmoluoC yb tesygrenE»telpirt«1,1,1,1=↑↑−=↓↓1,012=↑↓+↓↑nipsnoitcnufevaWnoitcnufevawcirtemmysitna :elpicnirp iluaPχ0,012==↑↓−↓↑ψψψψψ121221=−−+−−rrrrrrrrrRrRrRrRSGABABpalrevosmota :sdiloSAtomsfar away: nooverlapψ(r)⊗χ«singlet»spatialelpicnirp iluaP+noitcaretni bmoluoC :egnahcxecitengaM2onaN-1MscinortnipS

Exchange energy(twoions)antisymmetric(spin triplet→F)symmetric(spin singlet→AF)J (Coulomb) sets spin (magnetic) stateSpintronicsM1-NanoJ αoverlap3

1s7s27SpipExchange energyin atoms(Hund rule)65tnrdo1n0i0=l21x2s24scnf=l1=l3x2np2,32 7Xrra eaetrl=2, 2X54s24p63dntransition metalshM1-Nano41s2

LL↑↑↑↑↓↑↓↑LLLLψψψψψψ11()(1)()1(1)()rrrrrrrrAatomiclevelNM1-NanonSpintronicsgMost commonspin symmetriesisPPPPnSNPPnP=−=∏∏)()()(orrefitnaorref)dnab(snoitcnifevawtnereffidhtiw elbissoppalrevotnereffiDecittal a ni egnahcxE5

dnab d3)ecilsygrenerepsetatsforebmun(setatsfoytisneDhtdiwdnabdna etatsfoytisneD3d levelatomiclevelsNon-magneticmetalspin ↑and↓bandscoincideFermi surface isnotpolarizedMagneticmetal(Fe, Ni, Co…)spin ↑and↓bandsshiftedby exchangeenergyJ6M1-NanoThelargerthebandwidth, thelowerthedensityofstates3d bandnarrow, 4d and5d bandwide→3d transition metalsare magnetic4 and5d are not(Sboalinddlse)velsSpintronics

uCnadNCopper iedsntiyfosatetNickels3d bandfull3d bandpartiallyfilledFermi levelin wide4s bandFermi levelwheren(εF)smalln(εF)IslargeCondition to getferromagnetismn(εF)J>1SpintronicsStonercriterionM1-Nano7

dnabworran→SOD egraLεEEnJKxeFΔ+Δ>>00)(↑↓Δ=−=22222εσεENNnNnKFF)()()(,m↑↓=∫KJJEndεεεε)(desaercnisiygrenecitenik TUBΔ=−++−−=−xeEJNJNσσσ4112222222)()(NNN=+↑↓snortceleforebmuNεFN↑=∫εn(ε)dε−JεFN↑=∫εn(ε)dεJ8polarizationσ=N↑−N↓Npotentialenergy(exchange) gained22ΔEex=−J⎛⎜⎜N↑2−⎛⎜N⎞⎟⎞⎟⎟−J⎛⎜⎜N↓2−⎛⎜N⎞⎟⎞⎟⎟⎝⎝2⎠⎠⎝⎝2⎠⎠Shift 2J betweenspin ↑and↓bandSpin upgainSpin down gainytilibatsnirenotSonaN-1MscinortnipS

ps rofhtapeerfnaemtnereffid→,0,=↑↓↑↓σσεnF)(evoba 0Fεwoleb 1noitcnuf imreF feerfetats lanifdeipuccoetats laitini→∫=−σσεεdkffkkkk13'')()()(htapeerf-naemseitirupmifo noitartnecnoc :cecnatsiserotengamtnaiGn↓(εF)>n↑(εF)σ↓>σ↑⇒l↓<l↑oCM1-NanoSpintronicsl∝1,l∝1↑cn↑(εF)↓cn↓(εF)smalldiffusionlarge diffusion9↓,↑ ni

aVel-teFtromedlp(MultilayersofCu-Cosandwidchesassume nospin flip(R↑+R↓)4R↑R↓(R↑+R↓)2(R↑+R↓)2SpintronicsR~↑ciotiraM1-Nano)lResistanceratio(R↑4+RR↑↓)01

rehtOSpintronicsequivalentpictureM1-Nano(Landauer)11

Voir